How can I customize normal in this way?
Edinting normals will be implemented in the future, according to Blender Wiki.

You can try to use the split normals modifier on this way:

1) Create Empty Objects in the direction of your vertex normals.



2) Create a Group Vertex for those vertices which you want to have a perpendicular normal in the same face. For a cube you should create six groups, one per each main square face.



3) Create a Split Normals Modifier per each Group Vertex. Set mode to Directional , check Parallel Normals and select appropiate empty object for target and group vertex.



You will get an effect similar to rounded edges:



Finally you can apply all modifiers and your object will keep these normals.